In recent years, there has been considerable interest in carpet tiles. Carpet tiles offer considerable advantages over rugs or wall-to-wall carpeting which have been heretofore used extensively. For example, the use of carpet tiles for floor covering allows the removal of individual tiles which have become worn or soiled more than other tiles. Those tile which are not worn or soiled may be left in place. Additionally, tiles may be rearranged or replaced to enhanced decorative effects.
Carpet tile and carpet construction are well-known in the art and are shown for example in U.S. Pat. Nos. 3,402,094; 3,347,735; 3,764,448; 3,238,595; 2,776,233; 3,173,823; 3,309,259; 3,320,113; 3,515,622; 3,642,516, 3,120,023; and 3,014,829. In addition, carpet tiles of various constructions have been available commercially. A particularly advantageous carpet tile is disclosed and claimed in U.S. Pat. No. 4,010,301.
It has been suggested to include magnetic particles into floor coverings (other than carpet tiles) to enhance the attachment of the floor coverings to floors having at least one section which may contain a magnetically permeable metal. See for example, U.S. Pat. Nos. 4,184,304 and 3,341,996. The latter patent discloses forming a sheet of a minor amount of vinyl chloride and a major amount of barium ferrite by milling the materials together and then passing the mixture through a sheeting mill. The sheet is cut to tile size and laminated to the back of a thicker vinyl chloride tile sheet by hot pressing the sheets together. This procedure is relatively expensive due to the number and type of steps involved. In addition, lamination is difficult to control and two laminated sheets may separate during use, particularly when lateral stresses are applied to one sheet of the laminate. Separation of the two sheets, either complete or in part (which can result in bulging of the top sheet), makes the product unacceptable.
Various patents disclose methods of incorporating magnetic materials into thermoplastic or rubbery type materials. See for example, U.S. Pat. Nos. 989,967 and 3,051,988. It is also known to incorporate magnetic materials into wall coverings. See for example U.S. Pat. Nos. 3,609,934; 3,986,312; and 3,982,370.
It has been found that there exist manifold difficulties in forming carpet tiles including magnetized coatings even though the advantages of such a product are apparent. For example, the use of strips of magnetizable material such as disclosed in some of the prior art mentioned above, requires the fitting of such strips into preformed or subsequently formed carpet and/or carpet tile to avoid an uneven height of the carpet tile. Such a procedure is relatively difficult and costly. Similarly, lamination of a preformed sheet is relatively difficult and expensive.
It is similarly useful to include the magnetic materials in the lowest portion of the backing of the carpet tile since a lesser amount of material can be utilized to obtain the same amount of magnetic attraction that would be obtained than if the material were uniformly dispersed throughout the majority of the thickness of the carpet tile.
These problems are particularly acute with the production of flexible carpet tiles.
It has also been found very difficult to incorporate substantial amounts (that is, greater than 75% by weight) of magnetizable permanent magnetic materials such as the ferrites of the type MO.6Fe.sub.2 O.sub.3 where M is one or more of Ba, Sr, Ca or Pb, into many of the synthetic resinous materials used in manufacturing carpet tiles, particularly vinyl chloride plastisols. These magnetizable permanent magnetic materials are otherwise advantageous and desired for use in such articles.